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Unread 05-28-2020, 03:36 PM   #1
Wolverines
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Guidance/advice on raised shower base and pan

I've been reading this forum and learning quite a lot. I am in the process of refinishing a bathroom on the 3rd floor of my home (I'd consider myself an advanced DIYer - I'll eventually figure it out and take the time to do it right).

That leads me to my first post and seeking some guidance/advice to make sure I do the shower base/pan correctly. The prior shower was a small neo-angle prefab unit that leaked. I have removed that all, cleaned up the mold and mildew, and repaired the subfloor. Because of smaller floor joists, the existing shower drain pipe runs along the exterior wall just above the floor. So the shower drain is about 4" above the main subfloor and the shower base and pan will start from there, creating an ~8" step into the raised shower floor.

My plan is to build a 36"x48" raised subfloor out of 2x4's with plywood on top to create the shower floor. All glued and screwed together and to the main subfloor. The shower will have glass on 2 sides and tile on the other 2 sides and shower floor. For the shower pan, I was looking at using either a Kerdi or KBRS kit for the shower base and curb, and something like GoBoard for the walls. I need this to be waterproof and also have a concern about the weight of doing a traditional mud pan on top of the already built-up shower base. Does this plan sound reasonable? Anything I am not thinking about/missing that I should be considering?

Thank you in advance!
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Unread 05-28-2020, 07:31 PM   #2
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Welcome Jack.

8" is an almost huge step up into slower. Worse though is the exit. I sure wouldn't do it for a client. At the very least I'd think you'd want a "staging" platform half that height as an interim step.

A few questions:

1. Are those exterior walls?
2. Where are you geographically? Add that to your profile.
3. How big is room?
4. Is the upstream side of that drain leading to a vent?
5. Did you cut those studs off?
6. Will this job be inspected?

Let's start there and see where we go.
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Unread 05-28-2020, 09:49 PM   #3
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Welcome, jack.

I agree with Peter on the step. Not sure I like the staging platform much better.
Quote:
Originally Posted by Jack
Because of smaller floor joists, the existing shower drain pipe runs along the exterior wall just above the floor.
7. Do you plan to tile the floor outside the shower?

8. If yes, have you evaluated the "smaller" joist structure to see if it qualifies for a ceramic tile installation?

My opinion; worth price charged.
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Unread 05-28-2020, 09:57 PM   #4
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Thanks Peter! Not much I can do about the gap unless I find a way to get the curb down an inch or two. That's what was there prior, stepping into the neo angle shower.

1. Are those exterior walls?
The wall with the fiberglass batts (left side of pic) is exterior. The one with roxul is interior. Insulation was already there. Hard to see in the picture but the wall on the left with the batts is a total of 7.5" deep. It has 2"x4" studs on the exterior (150 years old). Someone built out the wall to 7.5" deep to accommodate the plumbing from what I can see.
2. Where are you geographically? Add that to your profile.
NJ, done.
3. How big is room?
It's an L shape, 10' on that exterior wall and 8' on that interior one. If I can get a sketch I'll upload it.
4. Is the upstream side of that drain leading to a vent?
The drain from the sink comes in from the right. To the left, it connects into the drain to go down and out of the house, but the toilet. The vent outside is near the toilet (so I guess that makes it downstream?)
5. Did you cut those studs off?
No, those studs cut were by a previous owner. They aren't holding anything up.
6. Will this job be inspected?
No inspection. I am moving the shower head and valve, but no other plumbing is moving. It's basically fixing the existing shower and tiling it.
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Unread 05-28-2020, 10:05 PM   #5
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Thanks CX.

7. Do you plan to tile the floor outside the shower?
Yes, I am planning to put tile over hardie backer. The floor was previously tiled on top of a thin bed or mortar and wire lathe. The joists below are ok, but I'm not sure how comfortable I would feel putting down a bed of mortar several inches thick. Maybe I'm being over cautious there.
8. If yes, have you evaluated the "smaller" joist structure to see if it qualifies for a ceramic tile installation?
To be honest, no. There was tile on the floor prior so I believe it can handle tile again. I just wasn't certain about building up the shower area then adding a bed of mortar on top of that given it previously only had a cheap fiberglass neo angle shower base.
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Unread 06-13-2020, 07:04 AM   #6
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Very slow progress here as I research and debate how to handle this unique shower situation. I realized I was asking for help but not giving enough to work from so I created a drawing to show the layout of the bathroom. Right now the shower drain location is offset to the left side and close to the corner.

I am leaning towards using a 38"x60" Kerdi shower tray. If I do, I will need to move the plumbing to center the drain (offset left), then cut off ~3" on the 2 sides of the tray to get the width down to ~32", and cut off 12" on the back (vanity side).

1 - is cutting the shower tray that way OK? Kerdi suggests cutting evenly on all sides. I would be able to get the 2 sides even but the back is far too long.

2 - to keep the curb lower (given the already raised pan), would I be better off cutting a Kerdi curb in half (to 3" height) or stacking Kerdi board to get to the same height?

Thanks again for the advice. I am going to start making some progress here!
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Unread 06-13-2020, 09:15 AM   #7
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Hi Jack. You can cut the Kerdi tray if you want but doing that will make the perimeter of the shower out of level since you'd be cutting more off one side than the others. Keeping the perimeter level looks best and makes the wall tiling easier. So, instead we usually recommend to mud the shower floor, that way you can keep the perimeter level and save some money at the same time.

Another thing, using the Kerdi tray means the plywood floor needs to be level first to keep the correct pitch from all directions to the drain. Having the plywood level doesn't matter if you mud it.
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Unread 06-13-2020, 08:55 PM   #8
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Thanks. I would expect that the back section of the shower slope (where I would cut off 12") would have a slightly different height. I might try and check it out in a store before I move ahead. The good thing is the section is against one of the curbs, which will have a glass wall above making it harder to see the slight height difference. I am very leery of doing mud and adding that kind of weight to the floor structure, which is why I am exploring all of the other options.
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Unread 06-13-2020, 09:42 PM   #9
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Jack, if your floor structure isn't suitable for a mud shower floor, it's not suitable for a tile shower at all. Are you planning to have a placard on the wall limiting use of the shower only to persons of a specific size? Or restricting the shower to use by only a single individual?
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Unread 06-14-2020, 06:19 AM   #10
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There was a neo-angle shower there before. I get that the preferred method is to put down a traditional pan liner and mud base. I guess I just don't love the idea of putting down 200lbs+ of concrete when there are other alternatives that can create a solid waterproof shower base that can be tiled.
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Unread 06-14-2020, 10:25 AM   #11
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A single sloped mud bed for a direct bonded waterproofing membrane-type receptor, starting with the minimum 3/4" of mud at your off-center drain is still gonna be under a hundred pounds in weight for that shower floor, Jack.

That does increase your floor's dead load, but if built to minimum standards, calculated with a dead load of 10psf and a live load of 40psf, that's unlikely to put you beyond the required L/360 deflection requirement.

Again, a single use by a full sized MIL is gonna cause you much more problem in that shower than will a sloped mud bed shower floor.

My opinion; worth price charged.
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Unread 06-14-2020, 09:01 PM   #12
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CX, that helps explain why I wasn't seeing what you were. I had double that in my estimate, assuming a pre-slope, shower liner, and mud pan with 1 1/4" at the drain. Hence a lot more weight.

So I could use less concrete in the mud pan by going with 3/4" at the drain and then putting something like a Kerdi membrane over it to waterproof. Doing that, I wouldn't need to move the drain from it's left offset position now. I would definitely use a Kerdi or KBRS curb and also waterproof the walls before tiling them.

What do you prefer to put on top of the plywood subfloor and under the mud?
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Unread 06-14-2020, 10:11 PM   #13
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Jack, my point was that it just doesn't matter at all. If you were to build a traditional receptor with mud/liner/mud and the minimum 1 1/2" top layer, you would indeed add more weight, but it still wouldn't matter so long as your joist structure is adequate for any shower construction at all.

Over your plywood subfloor you would put a cleavage membrane, which can be roofing felt or polyethylene sheeting or similar, then fasten minimum 2.5lb metal lath, then your sloped mud bed. That would be for either the pre-slope for a traditional receptor or for the only sloped mud bed for a direct bonded waterproofing membrane receptor. For a direct bonded membrane I would recommend you use more than the minimum 3/4" thickness at the drain, but you can get by with the minimum so long as your subfloor at the drain is well supported.

I would make the curb of stacked 2x4s in either method, too. For the traditional you would use metal lath and "fat mud" over the liner, for the direct bonded membrane method you would encase the curb in CBU prior to installing the membrane.

In any case, I would very strongly recommend you move the drain to the center of the shower footprint.

My opinion; worth price charged.
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Unread 09-17-2020, 10:21 AM   #14
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After a bit of a hiatus, I am close to putting in the mud pan as recommended. The plumbing lines are moved and tested and I moved the drain to as close to center as I could get (within an inch or two of center). I built the raised shower floor, which was glued and screwed into place. It's rock solid. The pan liner is in and has passed the water test so it's on to setting the mud pan. After I get the pan done I'll put the insulation back in the walls, put cement board up, move some electric, sheetrock one part and then I'll be ready for tile.

I know the pan is going to be the trickiest part for me but I've read enough on here and elsewhere that I can hopefully tackle it this weekend. I plan to use quickrete mud mix for the pan and stucco mix for the curb, which will attach to wire mesh that I will wrap over it and screw in from the outside only (so there are no punctures in the pan liner). Attached a few pictures.
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Unread 09-17-2020, 12:41 PM   #15
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1. The wall framing appears to be substantially missing at the ends of the shower curbs, Jack. What's your plan for fastening your CBU and wallboard outside the shower?

2. What sort of plywood is that you have on the shower floor?

3. You say you cantered the drain, but in your photo it appears far from the center of the shower footprint. What's up with that?

4. No blocking at all between the studs to support the pan liner?

5. No notching of the studs to accommodate the folds in the pan liner to allow your CBU to hang flat?

6. No dam corners for the pan liner at the ends of the curb?

7. Are the tops of the curb sloped to drain?

8. Pan liner looks pretty flat. No pre-slope under it? Always difficult to tell in photos.

9. You want "deck mud" for that top mud bed, not anything in a bag labeled mortar mix or mason's mix. If you'll look in our Liberry under the Shower Construction section you'll find some recipes for deck mud. What you want to end up with is a mix of about 5 parts sand and 1 part Portland cement and nothing else aside from a very little water.

The top mud bed wants to be a consistent thickness of at least 1 1/2 inches and follow the slope of the liner, which should be a minimum of 1/4-inch per horizontal foot.

My opinion; worth price charged.
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